1. Field of the Invention
This invention relates to vehicle wheel alignment apparatus, and particularly to the device of the apparatus which generates signals representative of the alignment position of the wheels.
2. Description of the Prior Art
Many different approaches have been tried for determining vehicle wheel alignment, some of which are all mechanical and some of which are electro-mechanical in make-up. In the relevant prior art, the mechanical devices are represented generally by the Manlove U.S. Pat. Nos. 3,164,910 of Jan. 12, 1965 and 3,181,248 of May 4, 1965. The mechanical components disclosed in these patents are arranged at the vehicle wheels and cooperatively connected by flexible lines for obtaining alignment data.
The electro-mechanical apparatus of the prior art is represented by such patents as MacMillan U.S. Pat. No. 3,443,318 of May 13, 1969, and Wilkerson U.S. Pat. No. 3,426,438 of Feb. 11, 1969. In these types of apparatus, electrical contacts are provided to make a circuit when the wheel position desired is reached. Somewhat more complex apparatus of the electro-mechanical character are represented by Senften U.S. Pat. No. 4,034,479 of July 12, 1977 and Hunter U.S. Pat. No. 4,106,208 of Aug. 15, 1978. These latter types generate signals which are fed into a console where meters display the information.
Some further relevant prior art is represented by Butler U.S. Pat. No. 3,865,492 of Feb. 11, 1975 which discloses apparatus using photo-electric receivers subject to a limited light source. In this same class is Hopkins et al U.S. Pat. No. 3,533,699 of Oct. 13, 1970, in which light responsive detectors are arranged to be activated more or less by the reflection of a light source off a mirror.
When alignment apparatus employs a light source which directly projects its beam toward detectors positioned at some distance, there is introduced the problem of obtaining the proper strength of the beam, and the further problem is also encountered of ambient light upsetting the signal strength or causing a false signal.